efanUser Guide


efan is a library for rendering Embedded Fantom (efan) templates.

Like EJS for Javascript, ERB for Ruby and JSP for Java, efan lets you embed snippets of Fantom code inside textual templates.

efan aims to hit the middle ground between programmatically rendering markup with web::WebOutStream and rendering logicless templates such as Mustache.

ALIEN-AID: Create powerful re-usable components with efanXtra and IoC !!!

ALIEN-AID: If rendering HTML, use Slim !!! The concise and lightweight template syntax makes generating HTML easy!

Quick Start

  1. Create a text file called Example.fan
    using afEfan
    class Example {
        Void main() {
            template := """<% ctx.times |i| { %>
                           <% } %>
                           Merry Christmas!"""
            text := Efan().render(template, 3)
            echo(text)  // --> Ho! Ho! Ho! Merry Christmas!
  2. Run Example.fan as a Fantom script from the command line:
    C:\> fan Example.fan
    Ho! Ho! Ho! Merry Christmas!


Efan supports the following tags:

Eval Tags

Any tag with the prefix <%= will evaluate the fantom expression and write it out as a Str.

Hello, <%= "Emma".upper %>!

Comment Tags

Any tag with the prefix <%# is a comment and will be left out of the resulting template.

<%# This is just a comment %>

Code Tags

Any tag with the prefix <% will be converted into Fantom code.

<% echo("Hello!") %>

Instruction Tags

The content of any tag with the prefix <%? is taken to be a Fantom using instruction.

<%? using concurrent::Actor %>

Escaping Tags

All efan tags can be escaped by adding an extra % character to the start and end tags. Example:

This is how you <%%= escape %%> efan tags.


This is how you <%= escape %> efan tags.


All whitespace in efan templates is preserved, except for when a line exists only to contain a code block (or similar). This has the effect of removing unwanted line breaks. For example:

Hey! It's
<% if (ctx.isXmas) { %>
<% } %>

is rendered as:

Hey! It's

and not:

Hey! It's



(Advanced users may turn this feature off in EfanCompiler.)

Template Context

Each template render method takes an argument called ctx which you can reference in your template. ctx is typed to whatever Obj you pass in, so you don't need to cast it. Examples:

Using maps:

ctx := ["name":"Emma"]  // ctx is a map

template := "Hello <%= ctx["name"] %>!"

Efan().render(template, ctx)

Using objs:

class Entity {
    Str name
    new make(Str name) { this.name = name }


template := "Hello <%= ctx.name %>!"
ctx      := Entity("Emma")  // ctx is an Entity

Efan().render(template, ctx)


All classes not in sys (and that includes all classes in your application) need to be referenced by their fully qualified class name:

<% concurrent::Actor.sleep(2sec) %>

Or imported with <%? using %> statements:

<%? using concurrent %>
<% Actor.sleep(2sec) %>

This is because compiled efan code resides in a newly constructed pod!

View Helpers

Efan lets you provide view helpers for common tasks. View helpers are classes or mixins that your efan template will extend, giving your templates access to commonly used methods. Example, for escaping XML:

mixin XmlViewHelper {
    Str xml(Str str) {

Set view helpers when calling efan:

Efan().render(template, ctx, [XmlViewHelper#])

Template usage would then be:

    Hello <%= xml(ctx.name) %>!

Err Reporting

Efan compilation and runtime Errs report snippets of code showing which line in the efan template the error occurred. Example:

Efan Compilation Err:
  file:/projects/fantom/Efan/test/app/compilationErr.efan : Line 17
    - Unknown variable 'dude'

    12: Five space-worthy orbiters were built; two were destroyed in mission accidents. The Space...
    13: </textarea><br/>
    14:         <input id="submitButton" type="button" value="Submit">
    15:     </form>
==> 17: <% dude %>
    18: <script type="text/javascript">
    19:     <%# the host domain where the scanner is located %>
    21:     var plagueHost = "http://fan.home.com:8069";
    22:     console.debug(plagueHost);

This really helps you see where typos occurred.

How efan Works

Efan works by converting the efan template string in to Fantom source code. It then compiles this source code into a new Fantom class. This new Fantom class extends any given ViewHelpers and has a hidden render() method. That is how code in the template is able to access the ViewHelpers.

Because types can not be unloaded, if you were compile 1000s of efan templates, it could be considered a memory leak.

Each invocation of Efan.compileXXX() creates a new Fantom type, so use it judiciously. Caching the returned EfanMeta classes is highly recommended. Example:

efanStr  := "<% ctx.times |i| { %>Ho! <% } %>"
template := Efan().compile(efanStr, Int#)  // <-- cache this!

ho       := template.render(1)
hoho     := template.render(2)
hohoho   := template.render(3)


When efan is added as a dependency to an IoC enabled application, such as BedSheet or Reflux, then the following services are automatically made available to IoC:

This makes use of the non-invasive module feature of IoC 3.